Generate Rsa Private Key Java
Contents
- 3. Saving the Keys in Binary Format
- Source Code
1. Introduction
Online RSA Key Generator. Key Size 1024 bit. 4096 bit Generate New Keys Async. RSA Encryption Test. Text to encrypt. RSA Decryption In Java. For decryption we will be using private key and we discussed above that the private key is generated in PKCS#8 format.Hence, following is the code to generate the private key from base64 encoded string using PKCS8EncodedKeySpec. The most popular Public Key Algorithms are RSA, Diffie-Hellman, ElGamal, DSS. Generate a Public-Private Key Pair. There are several ways to generate a Public-Private Key Pair depending on your platform. In this example, we will create a pair using Java. The Cryptographic Algorithm we will use in this example is RSA. #!usr/bin/env bash: openssl genrsa -out privatekey.pem 4096: openssl rsa -pubout -in privatekey.pem -out publickey.pem # convert private key to pkcs8 format in order to import it from Java.
but the online tools for generating RSA key pairs have different lengths output! The first picture shows public and private key in PEM format, encoded in Base64 (and not modulus and exponents of the key, which instead are shown in the second picture). The content of the RSA private key is as follows.
Let us learn the basics of generating and using RSA keys in Java. /generate-public-key-for-vagrant.html.
Java provides classes for the generation of RSA public and private key pairs with the package java.security. You can use RSA keys pairs in public key cryptography.
Public key cryptography uses a pair of keys for encryption. Distribute the public key to whoever needs it but safely secure the private key.
Public key cryptography can be used in two modes:
Encryption: Only the private key can decrypt the data encrypted with the public key.
Authentication: Data encrypted with the private key can only be decrypted with the public key thus proving who the data came from.
2. Generating a Key Pair
First step in creating an RSA Key Pair is to create a KeyPairGeneratorfrom a factory method by specifying the algorithm (“RSA” in this instance):
Initialize the KeyPairGenerator with the key size. Use a key size of 1024 or 2048. Currently recommended key size for SSL certificates used in e-commerce is 2048 so that is what we use here.
From the KeyPair object, get the public key using getPublic() and the private key using getPrivate().
3. Saving the Keys in Binary Format
Save the keys to hard disk once they are obtained. This allows re-using the keys for encryption, decryption and authentication.
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What is the format of the saved files? The key information is encoded in different formats for different types of keys. Here is how you can find what format the key was saved in. On my machine, the private key was saved in PKCS#8 format and the public key in X.509 Arma 3 activation key generator. format. We need this information below to load the keys.
3.1. Load Private Key from File
After saving the private key to a file (or a database), you might need to load it at a later time. You can do that using the following code. mac plus rom file download Note that you need to know what format the data was saved in: PKCS#8 in our case.
3.2 Load Public Key from File
Load the public key from a file as follows. The public key has been saved in X.509 format so we use the X509EncodedKeySpec class to convert it.
4. Use Base64 for Saving Keys as Text
Save the keys in text format by encoding the data in Base64. Java 8 provides a Base64 class which can be used for the purpose. Save the private key with a comment as follows:
And the public key too (with a comment):
5. Generating a Digital Signature
As mentioned above, one of the purposes of public key cryptography is digital signature i.e. you generate a digital signature from a file contents, sign it with your private key and send the signature along with the file. The recipient can then use your public key to verify that the signature matches the file contents.
Here is how you can do it. Use the signature algorithm “SHA256withRSA” which is guaranteed to be supported on all JVMs. Use the private key (either generated or load from file as shown above) to initialize the Signatureobject for signing. It is then updated with contents from the data file and the signature is generated and written to the output file. This output file contains the digital signature and must be sent to the recipient for verification.
6. Verifying the Digital Signature
The recipient uses the digital signature sent with a data file to verify that the data file has not been tampered with. It requires access to the sender’s public key and can be loaded from a file if necessary as presented above.
The code below updates the Signature object with data from the data file. It then loads the signature from file and uses Signature.verify() to check if the signature is valid.
And that in a nutshell is how you can use RSA public and private keys for digital signature and verification.
Source Code
Go here for the source code.
In order to be able to create a digital signature, you need a private key. (Its corresponding public key will be needed in order to verify the authenticity of the signature.)
In some cases the key pair (private key and corresponding public key) are already available in files. In that case the program can import and use the private key for signing, as shown in Weaknesses and Alternatives.
In other cases the program needs to generate the key pair. A key pair is generated by using the KeyPairGenerator class.
In this example you will generate a public/private key pair for the Digital Signature Algorithm (DSA). You will generate keys with a 1024-bit length.
Generating a key pair requires several steps:
Create a Key Pair Generator
The first step is to get a key-pair generator object for generating keys for the DSA signature algorithm.
As with all engine classes, the way to get a KeyPairGenerator object for a particular type of algorithm is to call the getInstance static factory method on the KeyPairGenerator class. This method has two forms, both of which hava a String algorithm first argument; one form also has a String provider second argument.
A caller may thus optionally specify the name of a provider, which will guarantee that the implementation of the algorithm requested is from the named provider. The sample code of this lesson always specifies the default SUN provider built into the JDK.
Put the following statement after the
line in the file created in the previous step, Prepare Initial Program Structure:
Initialize the Key Pair Generator
The next step is to initialize the key pair generator. All key pair generators share the concepts of a keysize and a source of randomness. The KeyPairGenerator class has an initialize method that takes these two types of arguments.
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The keysize for a DSA key generator is the key length (in bits), which you will set to 1024.
The source of randomness must be an instance of the SecureRandom class that provides a cryptographically strong random number generator (RNG). For more information about SecureRandom, see the SecureRandom API Specification and the Java Cryptography Architecture Reference Guide .
The following example requests an instance of SecureRandom that uses the SHA1PRNG algorithm, as provided by the built-in SUN provider. The example then passes this SecureRandom instance to the key-pair generator initialization method.
Some situations require strong random values, such as when creating high-value and long-lived secrets like RSA public and private keys. To help guide applications in selecting a suitable strong SecureRandom implementation, starting from JDK 8 Java distributions include a list of known strong SecureRandom implementations in the securerandom.strongAlgorithms property of the java.security.Security class. When you are creating such data, you should consider using SecureRandom.getInstanceStrong(), as it obtains an instance of the known strong algorithms.
Generate the Pair of Keys
The final step is to generate the key pair and to store the keys in PrivateKey and PublicKey objects.